Ionic liquid catalyst alkylation using a loop reactor

ABSTRACT

Provided is a process for producing low volatility, high quality gasoline blending components which comprises recirculation of at least a portion of a recovered stream comprising primarily isoparaffins. Recirculation of the stream allows for an enhanced I/O ratio and a more cost effective process.

FIELD OF ART

The present invention relates to a process for producing low volatility,high quality gasoline blending components which recirculates at least aportion of a recovered stream comprising isoparaffins to the process.More particularly, the present invention relates to an alkylationprocess utilizing an ionic liquid catalyst that produces a productcomprising gasoline blending components and recirculates at least aportion of a recovered stream comprising isoparaffins to the alkylationprocess.

BACKGROUND

Modern refineries employ many upgrading units such as fluid catalyticcracking (FCC), hydrocracking (HCR), alkylation, and paraffinisomerization. As a result, these refineries produce a significantamount of isopentane. Historically, isopentane was a desirable blendingcomponent for gasoline having a high octane (92 RON), although itexhibited high volatility (20.4 Reid vapor pressure (RVP)). Asenvironmental laws began to place more stringent restrictions ongasoline volatility, the use of isopentane in gasoline was limitedbecause of its high volatility. As a consequence, the problem of findinguses for by-product isopentane became serious, especially during the hotsummer season. Moreover, as more gasoline compositions contain ethanolinstead of MTBE as their oxygenate component, more isopentane had to bekept out of the gasoline pool in order to meet the gasoline volatilityspecification. So, the gasoline volatility issue became even moreserious, further limiting the usefulness of isopentane as a gasolineblending component.

An alkylation process, which is disclosed in U.S. Patent ApplicationPublication 2006/0131209, was developed that is capable of convertingthe undesirable, excess isopentane into desirable and much more valuablelow-RVP gasoline blending components. The contents of U.S. PatentApplication Publication 2006/0131209 are incorporated by referenceherein. This alkylation process involves contacting isoparaffins,preferably isopentane, with olefins, preferably ethylene, in thepresence of an ionic liquid catalyst to produce the low-RVP gasolineblending components. This process eliminates the need to store orotherwise use isopentane and eliminates concerns associated with suchstorage and usage. Furthermore, the ionic liquid catalyst can also beused with conventional alkylation feed components (e.g. isobutane,propylene, butene, and pentene).

The ionic liquid catalyst distinguishes this novel alkylation processfrom conventional processes for converting light paraffins and lightolefins to more lucrative products. Conventional processes include thealkylation of paraffins with olefins, and polymerization of olefins. Forexample, one of the most extensively used processes in the field is thealkylation of isobutane with C₃-C₅ olefins to make gasoline cuts withhigh octane number. However, this and all conventional processes employsulfuric acid and hydrofluoric acid catalysts.

Numerous disadvantages are associated with sulfuric acid andhydrofluoric acid catalysts. Extremely large amounts of acid arenecessary to initially fill the reactor. The sulfuric acid plant alsorequires a huge amount of daily withdrawal of spent acid for off-siteregeneration. Then the spent sulfuric acid must be incinerated torecover SO₂/SO₃ and fresh acid is prepared. While an HF alkylation planthas on-site regeneration capability and daily make-up of HF is orders ofmagnitude less, HF forms aerosol. Aerosol formation presents apotentially significant environmental risk and makes the HF alkylationprocess less safe than the H₂SO₄ alkylation process. Modern HF processesoften require additional safety measures such as water spray andcatalyst additive for aerosol reduction to minimize the potentialhazards. Thus, the ionic liquid catalyst alkylation process fulfills theneed for safer and more environmentally-friendly catalyst systems.

Benefits of the ionic liquid catalyst alkylation process include thefollowing:

(1) substantial reduction in capital expenditure as compared to sulfuricacid and hydrofluoric acid alkylation plants;

(2) Substantial reduction in operating expenditures as compared tosulfuric acid alkylation plants;

(3) substantial reduction in catalyst inventory volume (potentially by90%)

(4) a substantially reduced catalyst make-up rate (potentially by 98%compared to sulfuric acid plants)

(5) a higher gasoline yield

(6) comparable or better product quality (Octane number, RVP, T50)

(7) significant environment, health and safety advantages;

(8) expansion of alkylation feeds to include isopentane and ethylene;and

(9) higher activity and selectivity of the catalyst.

Ionic liquid catalysts specifically useful in the alkylation processdescribed in U.S. Patent Application Publication 2006/0131209 aredisclosed in U.S. Patent Application Publication 2006/0135839, which isalso incorporated by reference herein. Such catalysts arechloroaluminate liquid catalysts comprising an alkyl substitutedpyridium halide or an alkyl substituted imidazolium halide of thegeneral formulas A and B, respectively. Such catalysts further includechloroaluminate liquid catalysts comprising a hydrocarbyl substitutedpyridium halide or a hydrocarbyl substituted imidazolium halide of thegeneral formulas A and B, respectively.

where R═H, methyl, ethyl, propyl, butyl, pentyl or hexyl group and X isa haloaluminate and preferably chloroaluminate, and R₁ and R₂═H, methyl,ethyl, propyl, butyl, pentyl, or hexyl group and where R₁ and R₂ may ormay not be the same. Preferred catalysts include1-butyl-4-methyl-pyridinium chloroaluminate (BMP), 1-butyl-pyridiniumchloroaluminate (BP), 1-butyl-3-methyl-imidazolium chloroaluminate(BMIM) and 1-H-pyridinium chloroaluminate (HP).

However, the ionic liquid catalyst has unique properties, which requiresthat the ionic liquid catalyst alkylation process be further developedand modified to achieve superior gasoline blending component products,improved process operability and reliability, and reduced operatingcosts, etc. More particularly, the ionic liquid catalyst alkylationprocess requires uniform mixing of the hydrocarbon and catalyst,sufficient interfacial contact between the hydrocarbons and catalyst,good temperature and pressure control, and a high isoparaffin to olefin(I/O) ratio. In addition, alkylation by means of the ionic liquidcatalyst is an exothermic reaction requiring the removal of heatgenerated. Thus, it would be beneficial to the industry if an improvedalkylation process for converting isoparaffins and olefins in thepresence of an ionic liquid catalyst was available.

One technique that has been used in general alkylation processes is therecycling of effluent. For example, ExxonMobil's auto refrigerationprocess described at page 243 of Petroleum Refining—Technology andEconomics (3rd edition) by James Gary and Glenn Handwerk involvesrecycling catalyst and isobutane to the reactor where alkylation betweenthe olefins and isobutane takes place. U.S. Pat. No. 5,347,064 describesan isoparaffin-olefin alkylation process wherein recycled isobutane isadded to a series of alkylation reaction stages. U.S. Pat. No. 4,225,742discloses an HF alkylation process of isoparaffins with olefins whereinan alkane stream substantially free of alkylate (the product) andcomprising principally normal C₃ and C₄ paraffin hydrocarbons isrecycled to the reaction zone. However, the industry continues to strivefor improved, more efficient processes in order to lower the cost ofproducts, and in particular when using an ionic liquid catalyst.

SUMMARY

Provided is a process for producing low volatility, high qualitygasoline blending components incorporating recirculation of at least aportion of a recovered stream comprising primarily isoparaffins. Eitherall of the product or only a mere portion of the isoparaffins may berecirculated. In any case, the process includes the following steps:

(a) providing at least one olefin feed stream comprising olefins;

(b) providing at least one isoparaffin feed stream comprisingisoparaffins;

(c) contacting the at least one olefin feed stream with the at least oneisoparaffin feed stream in the presence of an ionic liquid catalyst inan alkylation zone under alkylation conditions to provide at least oneproduct stream, and

(d) recirculating to the alkylation zone a stream comprised primarily ofisoparaffin.

Among other factors, recirculation of a stream comprised primarily ofisoparaffin has been found to provide a more efficient and costeffective alkylation process when using an ionic liquid catalyst. Mostimportantly, the recirculation of a stream comprised primarily ofisoparaffin reactant allows the reaction in the presence of an ionicliquid catalyst to maintain a high effective I/O ratio, which minimizesundesired side reactions. One can also use a lower quality of feed whilemaintaining the high I/O ratio within the reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a first embodiment of presentinvention having an external loop for recirculation of primarilyisoparaffin.

FIG. 2 is a schematic illustration of a second embodiment of the presentinvention using a horizontal reactor with recycled vapor of primarilyisoparaffin.

DETAILED DESCRIPTION

The present invention provides a process for the production of lowvolatility, high quality gasoline blending components. According to thebroadest aspect of the present invention, the process involvesrecirculating a portion of at least one recovered stream from analkylation reaction comprised primarily of isoparaffin back to thealkylation reaction.

As used herein, the term alkylation reaction refers to the reaction thatoccurs between olefins and isoparaffins. The term “isoparaffin” meansany branched-chain saturated hydrocarbon compound, i.e. a branched-chainalkane with a chemical formula of C_(n)H_(2n+2). Examples ofisoparaffins are isobutane and isopentane. The term “olefin” means anyunsaturated hydrocarbon compound having at least one carbon-to-carbondouble bond, i.e. an alkene with a chemical formula of C_(n)H_(2n).Examples of olefins include ethylene, propylene, butene, and so on. Theolefins can comprise at least one olefin selected from the followingolefins: ethylene, propylene, butene, pentene, and mixtures of these.The isoparaffins can comprise at least one isoparaffin selected from thefollowing isoparaffins: isobutane, isopentane, and mixtures of these.

According to one aspect, the process begins by providing at least oneolefin feed stream comprising olefins and at least one isoparaffin feedstream comprising isoparaffins. The at least one olefin feed stream andthe at least one isoparaffin feed stream contact one another in thepresence of an ionic liquid catalyst within at least one alkylation zoneunder alkylation conditions. The term “alkylation zone” refers to thephysical area in which the alkylation between olefins and isoparaffinsoccurs. Interaction between the olefins and the isoparaffins under theinfluence of the catalyst provides at least one product streamcomprising the gasoline blending components. The at least one alkylationzone may be a single alkylation zone or a plurality of separate anddistinct alkylation zones.

The process thereafter requires that at least a portion of a recoveredstream comprised primarily of isoparaffin is recirculated to thealkylation zone. By primarily isoparaffin is meant a stream of at least50 volume % isoparaffin, and in another embodiment at least 70 volume %,and in yet another embodiment at least 90 volume %.

Referring to FIG. 1, a process is depicted which uses an external loopfor recirculating a stream comprised of primarily isoparaffin. Thehydrocarbon feeds 1, comprised of a isoparaffin feed and an olefin feedmixed together, is split and injected at three different points, 4, 5and 6, into the alkylation zone/reactor 7. Effluent 8 from the reactorgenerally comprises isoparaffin, catalyst and reaction product.Essentially all of the olefin is reacted, as the I/O(isoparaffin/olefin) ratio is maintained as high as practical in orderto insure complete reaction. At the beginning of the reaction processthe I/O ratio is generally around 10:1 as injected into the reactor 7.However, the effective ratio in the reactor, as the reaction occurs, canbe generally 1,000:1, or 10,000:1, or even higher, as almost all of theolefin is reacted and substantially only isoparaffin remains of thereactants.

The effluent 8 is then pumped via pump 9 through a heat exchange 10 inorder to remove reaction heat and help control the temperature in thereactor 7. Some part of the effluent can be separated and removed 11,while the remaining portion 12 comprised primarily of isoparaffin, isrecirculated to the reactor 7. Additional catalyst 13 can be added tothe recirculated stream.

By recirculating the stream of primarily isoparaffin, one can achieve aneffective high I/O ratio and insure product quality by employing a lowerI/O ratio in the feed, which is more cost effective. The recirculatedisoparaffin allows the charged I/O ratio to remain high while the ratioof newly added isoparaffin and olefin can be lower, for example 8:1, oreven 6:1. This results in a tremendous savings in isoparaffin cost.

Another embodiment is shown in FIG. 2, using a horizontal reactor.Isoparaffin 21 is injected into the reactor 22 at a first nozzle 23.Catalyst 24 is also injected at nozzle 23. Olefin 25 is injected intothe reactor at multiple olefin injection points 26, which increases theinternal I/O ratio and provides improved mixing inside the reactor. Thehorizontal reactor is generally run at low pressure so that reactionheat is removed by isoparaffin evaporation. The generated vapor providesextra mixing inside the reactor, and the isoparaffin vapor is removed at27 and fully condensed in a condenser 28 and recycled 29 back to thereactor 22. Product is removed at 30.

It should be appreciated that the olefins and isoparaffins need notexist in separate olefin feed stream(s) and the isoparaffin feedstream(s). Rather, the olefins and isoparaffins can be mixed orotherwise combined to form one or more hydrocarbon feed stream(s). Thus,at least one hydrocarbon feed stream can comprise the at least oneolefin feed stream and the at least one isoparaffin feed stream.

Alkylation is a exothermic reaction. Thus, it is necessary to removeheat from the at least one alkylation zone by some means in order tomaintain the desired reaction temperature or temperature range. Avariety of methods are available for removing such reaction heat andmaintaining control of the reaction temperature in the alkylation zone.One method of cooling the at least one alkylation zone involves passingthe at least one product stream (or part of the at least one productstream) through at least one heat exchanger. This method is illustratedand discussed above in relation to FIG. 1. Another method of cooling theat least one alkylation zone involves evaporation. In this method, asdepicted in FIG. 2, reaction heat is removed instantly by isoparaffinevaporation within the alkylation. Other conventional methods, such ascooling jackets, can also be used as are known in the art.

The non-recirculated portion of a product stream(s) may be treated byany known separation technique in order to separate the gasolineblending components from the other constituents in the productstream(s). Generally, the catalyst and hydrocarbon phase, whichcomprises unreacted isoparaffins and the gasoline blending components,are first separated. Next, the gasoline blending components areseparated from the remainder of the hydrocarbon phase. A variety offeasible separation methods are known in the art. An example of a usefulmethod of separating the gasoline blending components from hydrocarbonphase is distillation.

The present process employs an ionic liquid catalyst. Ionic liquidcatalysts are well known in the art.

The process can employ a catalytic composition comprising at least onealuminum halide and at least one quaternary ammonium halide and/or atleast one amine halohydrate. An example of an aluminum halide which canbe used in accordance with the invention is aluminum chloride.Quaternary ammonium halides which can be used in accordance with theinvention are described in U.S. Pat. No. 5,750,455, which isincorporated by reference herein, which also teaches a method for thepreparation of the catalyst. An exemplary ionic liquid catalyst isN-butylpyridinium chloroaluminate (C₅H₅NC₄H₉Al₂Cl₇).

The ionic liquid catalyst can also be a pyridinium or imidazolium-basedchloroaluminate ionic liquid. These ionic liquid have been found to bemuch more effective in the alkylation of isopentane and isobutane withethylene than aliphatic ammonium chloroaluminate ionic liquid (such astributyl-methyl-ammonium chloroaluminate). The ionic liquid catalyst canbe a chloroaluminate ionic liquid catalyst comprising a hydrocarbylsubstituted pyridinium halide or a hydrocarbyl substituted imidazoliumhalide. Alternatively, the ionic liquid catalyst can be achloroaluminate ionic liquid catalyst comprising an alkyl substitutedpyridinium halide or an alkyl substituted imidazolium halide. Morespecifically, the ionic liquid catalyst may be selected from the groupconsisting of:

a chloroaluminate ionic liquid catalyst comprising a hydrocarbylsubstituted pyridinium halide mixed in with aluminum trichloride or ahydrocarbyl substituted imidazolium and aluminum trichloride preferablyin 1 molar equivalent hydrocarbyl substituted pyridinium halide orhydrocarbyl substituted imidazolium halide to 2 molar equivalentsaluminum trichloride of the general formulas A and B, respectively;

a chloroaluminate ionic liquid catalyst comprising an alkyl substitutedpyridinium chloride and aluminum trichloride or an alkyl substitutedimidazolium chloride and aluminum trichloride preferably in 1 molaralkyl substituted pyridinium chloride or alkyl substituted imidazoliumchloride to 2 molar equivalents of aluminum trichloride of the generalformulas A and B, respectively;

and mixtures thereof,where R═H, methyl, ethyl, propyl, butyl, pentyl or hexyl group and X isa haloaluminate and preferably a chloroaluminate, and R₁ and R₂═H,methyl, ethyl, propyl, butyl, pentyl, or hexyl group and where R₁ and R₂may or may not be the same.

Preferably the ionic liquid catalyst is selected from the groupconsisting of 1-butyl-4-methyl-pyridinium chloroaluminate (BMP),1-butyl-pyridinium chloroaluminate (BP), 1-butyl-3-methyl-imidazoliumchloroaluminate (BMIM), 1-H-pyridinium chloroaluminate (HP), andN-butylpyridinium chloroaluminate (C₅H₅NC₄H₉Al₂Cl₇).

A metal halide may be employed as a co-catalyst to modify the catalystactivity and selectivity. Commonly used halides for such purposesinclude NaCl, LiCl, KCl, BeCl₂, CaCl₂, BaCl₂, SiCl₂, MgCl₂, PbCl₂, CuCl,ZrCl₄, and AgCl as published by Roebuck and Evering (Ind. Eng. Chem.Prod. Res. Develop., Vol. 9, 77, 1970). Preferred metal halides areCuCl, AgCl, PbCl₂, LiCl, and ZrCl₄.

HCl or any Broensted acid may be employed as an effective co-catalyst toenhance the activity of the catalyst by boosting the overall acidity ofthe ionic liquid-based catalyst. The use of such co-catalysts and ionicliquid catalysts that are useful in practicing the present invention aredisclosed in U.S. Published Patent Application Nos. 2003/0060359 and2004/0077914. Other co-catalysts that may be used to enhance thecatalytic activity of the ionic liquid catalyst include IVB metalcompounds preferably IVB metal halides such as TiCl₃, TiCl₄, TiBr₃,TiBr₄, ZrCl₄, ZrBr₄, HfC₄, and HfBr₄ as described by Hirschauer et al.in U.S. Pat. No. 6,028,024.

Alkylation conditions are maintained in the at least one alkylationzone. The molar ratio between the isoparaffin and the olefin is in therange of 1 to 100, for example, advantageously in the range 2 to 50,preferably in the range 2 to 20. Catalyst volume in the reactor is inthe range of 2 vol % to 70 vol %, preferably in the range of 5 vol % to50 vol %. The reaction temperature can be in the range −40° C. to 150°C., preferably in the range −20° C. to 100° C. The pressure can be inthe range from atmospheric pressure to 8000 kPa, preferably sufficientto keep the reactants in the liquid phase. Residence time of reactantsin the at least one alkylation zone is in the range of a few seconds tohours, preferably 0.5 min to 60 min.

Typical alkylation conditions may include a catalyst volume in the atleast one alkylation zone of from 5 vol % to 50 vol %, a temperature offrom −10° C. to 100° C., a pressure of from 300 kPa to 2500 kPa, anisoparaffin to olefin molar ratio of 2 to 10 and a residence time of 1minute to 1 hour.

Although the present invention has been described in connection withpreferred embodiments thereof, it will be appreciated by those skilledin the art that additions, deletions, modifications, and substitutionsnot specifically described may be made without departing from the spiritand scope of the invention as defined in the appended claims.

1. A process for the production of low volatility, high quality gasoline blending components comprising: (a) providing at least one olefin feed stream comprising olefins; (b) providing at least one isoparaffin feed stream comprising isoparaffins; (c) contacting the at least one olefin feed stream with the at least one isoparaffin feed stream in the presence of an ionic liquid catalyst in an alkylation zone under alkylation conditions to provide at least one product stream; and (d) recirculating to the alkylation zone a stream comprised of primarily isoparaffin.
 2. The process according to claim 1, wherein the olefin feed stream comprise at least one olefin selected from the group consisting of ethylene, propylene, butene, pentene, and mixtures thereof.
 3. The process according to claim 1, wherein the isoparaffin feed stream comprise at least one isoparaffin selected from the group consisting of isobutane, isopentane, and mixtures thereof.
 4. The process according to claim 1, further comprising: passing a product stream through at least one heat exchanger; and removing heat from the product stream.
 5. The process according to claim 1, wherein the stream comprised of primarily isoparaffin is separated from effluent obtained from the contacting in step (c).
 6. The process according to claim 1, wherein the stream comprised primarily of isoparaffin is condensed from vaporous overhead in a horizontal reactor in which the contacting in step (c) occurs.
 7. The process according to claim 1, wherein the ionic liquid catalyst is selected from the group consisting of: a chloroaluminate ionic liquid catalyst comprising a hydrocarbyl substituted pyridinium halide or a hydrocarbyl substituted imidazolium halide of the general formulas A and B, respectively; a chloroaluminate ionic liquid catalyst comprising an alkyl substituted pyridinium halide or an alkyl substituted imidazolium halide of the general formulas A and B, respectively;

and mixtures thereof, where R═H, methyl, ethyl, propyl, butyl, pentyl or hexyl group and X is a haloaluminate and preferably a chloroaluminate, and R₁ and R₂═H, methyl, ethyl, propyl, butyl, pentyl, or hexyl group and where R₁ and R₂ may or may not be the same.
 8. The process according to claim 7, wherein the ionic liquid catalyst is selected from the group consisting of 1-butyl-4-methyl-pyridinium chloroaluminate (BMP), 1-butyl-pyridinium chloroaluminate (BP), 1-butyl-3-methyl-imidazolium chloroaluminate (BMIM), 1-H-pyridinium chloroaluminate (HP), and N-butylpyridinium chloroaluminate.
 9. The process according to claim 7, wherein the catalyst further comprises an HCI co-catalyst.
 10. The process according to claim 1, wherein there are multiple injections of olefin into the alkylation zone.
 11. The process according to claim 1, wherein there are multiple injections of isoparaffin into the alkylation zone.
 12. The process according to claim 1, wherein the I/O ratio of newly added reactants injected into the alkylation zone is in the range of from 6:1 to 10:1. 